Measurement of secondary tracers in FDG tumor imaging by rapid multi-tracer PET

Rapid multi-tracer PET, where two to three PET tracers are rapidly scanned with staggered injections, can recover certain imaging measures for each tracer based on differences in tracer kinetics and decay. We previously showed that single-tracer imaging measures can be recovered to a certain extent from rapid dual-tracer ⁶²Cu-PTSM (blood flow) + ⁶²Cu- ATSM (hypoxia) tumor imaging. Here we develop improved tracer-separation algorithms and evaluate signal-separation performance for rapidly imaging various combinations of F- FDG plus ⁶²Cu-PTSM and/or ⁶²Cu-ATSM. Dynamic imaging with these three tracers was performed in four dogs with prexisting tumors, and the raw scan data was combined to emulate dual- and triple-tracer imaging, using the single-tracer scans as gold standards. The multi-tracer data were processed for static (SUV) and kinetic (k₁-k₃, knet) endpoints for each tracer, followed by linear regression analysis of multi-tracer vs. single-tracer results. The FDG information was largely retained in these multi-tracer protocols. Static imaging measures (SUV) for FDG were accurately recovered, with r>0.99 in all protocols studied (four dual-tracer and one triple-tracer). Dynamic FDG imaging measures (k!-k3, knet) were well-correlated with single-tracer values (r>0.99). SUVs for PTSM and ATSM were also recovered well (r=0.97 and 0.92, respectively), and dynamic measures were recovered to varying degrees. The additional and complementary information obtained from PTSM and ATSM imaged simultaneously with FDG has the potential to improve tumor assessment for image-guided therapy and monitoring, warranting further development of the signal-separation algorithms.